This invention relates to cleaning of enclosed gear train housings, particularly motor operated valve gear train housings and more particularly to methods and devices for cleaning and removing lubricant from such gear train housings without disassembly of the gear train.
Enclosed gear trains are used in conjunction with motor operated valves. A motor operated valve is a valve that is operated by a series of gears, which can be driven by a motor. The motor can be electric, pneumatic, or hydraulic, although the most prevalent type is an electric motor. The gears are chosen based on the application of the valve. The motor operated valve is used for the quick, remote operation of valves and for the operation of large valves. It can be actuated by manual application of power to the motor or by automatic application of power. The motor operated valve can also be manually operated using a hand wheel.
Motor operated valves can be obtained as motor operators. A motor operator can comprise a valve, a motor, a gear train, a torque limiting mechanism and a housing therefor. Such a motor operator combination is available commercially under the trademark LIMITORQUE, for nuclear power plant applications. The motor operator can function as follows: An electric motor turns the gears which amplify the torque to a point necessary to drive the valve stem between open and closed positions. The travel of the valve stem can be limited by limit switches and/or torque limiting (sensing) mechanisms that may be contained in or on the operating mechanism housing which contains the gears. Normally, the same lubricant that lubricates the gears also lubricates the torque limiting mechanism.
Motor operated valves generally operate on a non-continuous cycle. The valve operating mechanisms, such as LIMITORQUE, may be used to drive a variety of types and sizes of valves. These valves are normally used where remote control is necessary or desirable. Gear reduced high torque motors for this purpose are used in highly critical services such as in nuclear and other power plants, refineries, space vehicle launch facilities and the like.
Lubricants, normally heavy greases which may include complex chemicals, are used to lubricate the gear trains. The lubricant for use in a motor operated valve system is typically a grease which adheres to the gears and any torque limiting mechanism without the need for an external force to keep the grease in place on the gears and other mechanisms during normal operating conditions. As a result, the lubricating greases for use under ambient conditions are typically semi-solid or more consistent under ambient conditions. In general, the semi-solid or thicker greases are used for motor operated valves, namely, ones having a grade as measured by ASTM consistency grade 85-115 or more or National Lubricating and Grease Institute (NLGI) consistency grade of 6 or less. A preferred lubricant for use in the LIMITORQUE mechanism used in nuclear power plants is one having an NLGI grade equal to 0; for example, the grease sold as Nebula EPO (Exxon). In general, the grade of grease used is specified by the manufacturer of the motor operator. The term "lubricant grease" used here thus refers to a lubricant of naturally occurring and/or synthetic components having a consistency at temperatures and pressures under which the lubricant is used, i.e., under ambient conditions such that the lubricant grease adheres to the lubricated components without the need for an external force to contain the grease on the components to be lubricated. Lubricant grease is distinguished from a lubricant oil, which is unsuitable for use with a motor operated valve which requires a more consistent lubricant and whose housing would not retain the oil.
Over time, the lubricating capacity of the lubricants is reduced due to degradation resulting from radiation, age, humidity and other known causes. It is thus necessary to remove the lubricant from the gear train housing to facilitate relubrication. Relubrication can improve the predictability and life of the gear train. Improper valve operation or failure, which can be precipitated by reduced operability or failure of the gear drive due to inadequate lubrication, can cause unacceptable levels of risk or maintenance shutdown of the facility.
The ability, desire and means of effectively removing a large percentage of the lubricant from a motor operated valve or other heavy mechanical gear train housing is substantially influenced by the purpose of the gear train, the cost of facility shutdown for cleaning, hazards to service personnel, including radiation and steam or chemical explosion, alternatives to lubrication and relubrication and the risk of improper assembly if the valve gear train housing is open and disassembled to effect cleaning and inspection.
The enclosed gear train housings for motor operated valves or other heavy mechanical gear train housings used in commercial applications are typically cleaned and relubricated by removing the gear housing from the valve to a shop for disassembly or to disassemble the gear train in place and relubricate. Disassembly requires that the valve be out of operation for extended periods of time. This lack of operation results in the inability to operate other systems and equipment. Further, disassembly can result in incorrect reassembly.
The invention described herein provides an inexpensive and quick alternative for cleaning enclosed gear train housings for motor operated valves, in situ, without disassembling the gear train, which comprises cleaning the gear train housing in situ by removing bulk lubricant by suction, as an optional step, dislodging and dissolving any remaining lubricant with a fluid lance containing solvent for the lubricant, then removing any remaining lubricant/solvent mixture.
U.S. Pat. Nos. 1,549,952, 1,696,100, 2,011,811 and 3,308,840 all describe devices for automobile gear casings and other enclosed systems of automobiles. The gear lubricants used for automobile systems are liquids. The efficiency of the cleaning, namely, how much of the spent lubricant is removed, is not particularly critical in an automobile system. The lubricant used within a gear train housing for a motor operated valve is a grease. The difference in form is due to the fact that the gears involved are high torque gears requiring thick lubricants, in a solid or semi-solid form rather than liquid form. In addition, because these motor operated valves are used in essential services such as nuclear and other power plants, refineries, space vehicle launch facilities and the like, where lubricant failure can result in shutdown of the facility, it is absolutely essential that cleaning efficiency be greater than 90% and preferably almost 100%. The cited prior art does not use in-place cleaning for enclosed gear trains of motor operated valves or high torque gears which utilize a lubricant grease. It has been surprisingly found that the method of this invention can have a cleaning efficiency in excess of 99%.
U.S. Pat. No. 2,685,347 and French Patent No. 2,025,982 relate to cleaning of gear cases in oil field applications. Here again, the lubricant is an oil, as seen from the passage in column 1, lines 11-15, of U.S. Pat. No. 2,685,347.
U.S. Pat. Nos. 2,691,380, 4,361,282 and 4,479,612 all relate to various types of flushing tools. U.S. Pat. No. 2,665,772 relates to a lubrication system having a pressured feed and suction. U.S. Pat. No. 3,585,654 relates to a quick-disconnect joining element.